Further understanding of chest wall mechanics, especially in pathologic states, requires a better understanding of the significance of inspiratory muscle pressure-flow behavior than we now have; however, this issue has been largely overlooked. For example, the respiratory pump usually operates closer to the high flow - low pressure (high velocity) region of its force-velocity range, but most studies of inspiratory muscle performance constrain the muscles to operating at the high pressure - low flow (high force) region. Our laboratory has been actively investigating inspiratory muscle performance at both ends of the force-velocity range. by devising ventilatory tasks with varied combinations of pressure flow that can be sustained for equal times, we have demonstrated the importance of pressure and flow to endurance. Mechanisms here reflect either 1) the force-velocity characteristics of the muscle or 2) the roles of the major inspiratory muscle groups (RC muscles and diaphragm) which may vary with lung volume, pressure-loading and flow-loading. The goal of the present proposal is to elucidate these mechanisms. this will be accomplished by characterizing the pressure-flow-volume relationships during single maximal inspiratory efforts and probing how these relationships re altered by sustained pressure-loaded or flow-loaded tasks, specifically loading the rib cage muscles or diaphragm, hyperinflation, and altered neural drive. Predictations based on knowledge of force-velocity-length behavior, and on knowledge of chest wall mechanics will serve to differentiate between these mechanisms. Accordingly, once completed these experiments will provide insight into the mechanics determining pressure-flow-volume performance of the inspiratory muscles.